1. Field of the Invention
The present invention relates to a gateway for connecting networks of different types and generating information for use in charging fees, and also to a system for charging fees for communication between networks of different types, by using the gateway connecting networks of different types.
2. Description of the Related Art
In some cases, a TV-telephone talk is performed between a mobile telephone and a session initiation protocol terminal (hereinafter referred to as “SIP terminal”), wherein the mobile telephone is represented by the third-generation telephone (3G-324M) that enables transmission and reception of images and sound.
The network to which the third-generation telephone is connected (hereinafter referred to as “3G network”) and the Internet service-provider network to which the SIP terminal is connected (hereinafter referred to as “ISP network”) are of different types. The 3G network and ISP network may use different signal formats. More specifically, they may differ in terms of call connection mode and audio/video CODEC (COder DECoder).
In some cases, a gateway is used to connect the 3G network and the ISP network. The gateway has a signaling gateway (SGW) function of converting the call connection mode to accomplish call connection and a media gateway (MGW) function of converting audio/video CODEC to achieve media connection. The gateway converts signals received from one network to signals suitable for the signal format of the other network. This makes it possible to perform communication between the networks of different types.
In communication such as the TV-telephone communication, a C-Plane for controlling a call control and a U-Plane for achieving media communication are utilized. Networks of different type differ in terms of the system of controlling the C-Plane and the data format of the U-Plane. Inevitably it is necessary to use an interface that connects the C-Plane and the U-Plane, in order to accomplish communication between such networks of different types. Thus, an SGW converts the C-Plane, and an MGW converts the U-Plane.
A type of a network, an ISP network in particular, may have no system of charging fees on the basis of communication time. The network may otherwise have no system of charging fees for the connection to the network. On the other hand, fees are generally charged for the connection to the 3G network, on the basis of communication time. Hence, fees cannot be charged, in some cases, to a user of the SIP terminal, for the communication with the 3G terminal which has been initiated by call from the SIP terminal.
In a type of a network, an ISP network in particular, packet communication is employed. Video data and audio data are transmitted in the form of packets. Path for the packets of audio and video data cannot be uniquely identified. This makes it difficult, in some cases, to determine how long a single telephone talk has lasted.
In the conventional telephone communication, CELP (Code-Excited Linear Prediction) is used to perform audio coding if the communication is proceeding between fixed telephones, between G.711 phones or between PDCs (Personal Digital Cellular) Thus, the CODEC used in the communication can be uniquely determined from the terminals used. Recently, however, each terminal may have a plurality of CODECs. To accomplish communication between terminals of different types, the ability of one terminal is compared with the ability of the other terminal and ability exchange is effected in some cases to select a CODEC common to both terminals. In many cases, the ability exchange is carried out after the call connection by the U-Plane that is a path for audio and video media. In the phase of exchanging the ability, the fee-charging system on the calling side may start charging fee in some cases when the data passes through the U-Plane. If no CODECs that enable talks are available as the result of the ability exchange, however, any talk will be impossible and the call will be cut. Assume that it takes one second to exchange the ability and that the fee is charged in units of, for example, three minutes. Then, the fee for three minutes will be charged for the ability exchange, though the users cannot talk at all.
It is desired that the fee-charging be started when the end-to-end (terminal to terminal) connection is achieved, making communication possible.
An invention relating to a network system has been made (for example, see JP-A-2001-358777). In the network system, the IP (Internet Protocol) packet that accords with the service demanded by a terminal is transmitted to a service provider via a plurality of IP networks of different protocols. Then, the service is supplied to the terminal by using the IP packet transmitted from the service provider via the plurality of IP networks. This network system is characterized in that a packet-converting means is provided between the IP networks. The packet-converting means converts the format of any transmitted IP packet to the format of the IP network to which the IP packet should be sent.
A data-distribution system is disclosed (for example, see JP-A-2002-176637). This system comprises at least a user terminal and a contents server, which are connected via a network. In the system, contents data is distributed from the contents server to the user terminal at the request of the user terminal. The system has an authentication device that is connected via the network and issues digital identification information to the user terminal and the contents server; a data-converting device that converts, at the request of the user terminal, the data-conversion device the contents data to data of such a format that the user terminal can process; and a fee-charging device that charges fee for the distribution of contents data and the conversion of the contents data, at the requests made by the contents server and data-converting device. The user terminal, the data-converting device and the fee-charging device can transmit and receive data when they are successfully authenticated on the basis of the digital identification information issued from the authentication device.
A communication system is disclosed (for example, see JP-A-2002-176445). This system comprises a plurality of communication networks of different communication schemes, to which mobile terminals can be connected and which can be connected via the Internet by using the Internet protocol. The system has a service network that manages the fee-charging information about the mobile terminals and provides service to the mobile terminals; an HA (Home Agent) device of mobile IP (Internet Protocol) that is provided in the service network, always manages to determine in which network each mobile terminal exists and distributes received data to an appropriate network via the Internet; and FA (Foreign Agent) devices of mobile IP that transmit, each provided in one communication network and designed to transmit a position-registering request to the HA device, and to transfer data received from the HA device via the Internet to the mobile terminal. Note that the position-registering request has been made to register the position of the mobile terminal that exists in the communication network. In this system, the communication between the communication networks and the communication relay over the communication networks can be freely accomplished by using the position-registering request exchanged between the HA device and the FA devices and the responses to the position-registering request.